Oil with a specific gravity of 0.72 is used as the indicating fluid in a manometer.

the difference in oil levels is 0.850 m

Explanation:

given data

specific gravity ρ = 0.72

pressure across P = 6 kPa = 6000 Pa

solution

we get here difference in oil levels h is

P = ρ × g × h   .................1

here ρ = 0.72 × 1000 = 720 kg/m³

and g is 9.8  

put here value in equation 1  and we get h

6000 = 720  × 9.8 × h

h =  

h = 0.850 m

so the difference in oil levels is 0.850 m

4 days to complete the work.

Explanation:

6 MEN OR 8 WOMEN

means that each man completes the 1/(6*12) of the work per day

OR each women completes 1/(8*12) of the work per day

9 MEN AND 12 WOMEN completes …..

9 * 1/(6*12) + 12* 1/(8*12) of the work per day.

Note that we add these 2 fractions because of the word ‘AND’ .

that gives us a simple fraction of 1/4 of the work per day.

Thus reversing it, gives you time taken = 4 days to complete the work.